The naphtha boiling range hydrocarbons sold commercially as gasoline are normally a blend of several streams produced in a petroleum refinery. These include reformates and alkylates which are relatively sulfur free because of upstream refining. Another major source of the naphtha boiling range hydrocarbons are processing units which do not receive a highly desulfurized feed. These include hydrocracking units, coking units and fluidized catalytic cracking (FCC) process units. A perpetual goal of the refining industry is to increase octane of its products. The present invention discloses a process for increasing the octane of naphtha boiling range hydrocarbons by separating the hydrocarbons and isomerizing those that may be readily isomerized into high octane products.
The dividing wall or Petlyuk configuration for fractionation columns was initially introduced some 50 years ago by Petlyuk et al. Dividing wall columns have been employed for the separation of hydrocarbon mixtures as evidenced by the disclosure of U.S. Pat. No. 2,471,134. It has been recognized that in specific circumstances the use of dividing wall columns is desirable over conventional fractionation columns. For instance, a commercialization of a fractionation column employing this technique is described in the article appearing at page s14 of a supplement to The Chemical Engineer, 27 Aug. 1992.
U.S. Pat. No. 2,471,134 illustrates a dividing wall fractionation column having a partition or dividing wall 20 dividing the trayed column into two parallel vapor-liquid contacting chambers. A similar but more detailed disclosure of a dividing wall fractionation column is provided by U.S. Pat. No. 4,230,533. Dividing wall columns are closely related to a different type of column referred to as a partitioned distillation column such as illustrated in U.S. Pat. No. 5,755,933. A partitioned distillation column differs from a dividing wall column in that the vertical dividing wall is positioned such that it contacts one end of the column. Thus only one terminal portion of the column is divided into the two parallel contacting sections. In this manner two overhead products or two bottom products may be removed from a single column. A dividing wall column produces an intermediate boiling fraction.